yes, a very annoying problem. This happens if you have more than one copy of Photoshop available. For example, your backup drive is mounted with a copy of PS on it.
For some very odd reason, when launching PS from LR, it does not always default to the copy of photoshop that resides in the same application folder LR is located in. Even if you have PS running in the background it will often try to launch a different copy (with the annoying PS has moved dialog).
Oddly if I open open to merge to panorama, it opens the correct copy of PS.
Iíve found no way to avoid this other than to make sure no other copies of PS are available. My backup scripts now all exclude the PS app itself, just backs up everything else in the PS folder. I decided I didnít need a backup copy of PS anyway.